The invention concerns a rolling method and line for any section or metal profile, such as for example, railway lines, starting from billets or blooms, which provides the use of a reversible edging stand (RES) combined with a two-high reversible roughing stand or Break-Down Mill (BDM) and positioned upstream or downstream thereof. Using the RES allows the use of a single BDM stand, irrespective of the starting material, reducing the number of rolling passes in the BDM stand and in all the steps of the rolling sequence.
It is well-known that to roll rails and other sections, starting from billets or blooms, a roughing step has to be carried out before the finishing step.
It is also well-known that such roughing step can be carried out using two BDM stands, respectively BDM1 and BDM2 arranged in series, which can have plane and/or shaped rolls, arranged in various ways.
In accordance with a first conventional solution, shown schematically in FIG. 1, the BDM1 stand has two grooved profiles (PS1 and PS2) and is used only for plane passes, while the BDM2 stand, which has a series of six grooved profiles (from PS3 to PS8), is used as a stand to prepare shaped pieces for the subsequent finishing train. This solution entails wide roller tables, about 2.5-3 m, which represents a limit which is difficult to overcome, due to the excessive weight which the rolls would otherwise have, and also due to the constructional complexity, which would weigh on the movement members of the rolls and cause inherently high costs. Therefore, considering the size of the rolls, usually no wider than 3 m, and the size of the sections to be rolled, each rolling roll is provided at most with six grooved profiles.
In accordance with a second conventional solution, shown schematically in FIG. 2, the stands BDM1 and BDM2 have only four grooved profiles each (respectively from PS1 to PS4 and from PS5 to PS8) to allow reducing the width of the roller table.
The state of the art also includes the use of a roughing train of the so-called xe2x80x9copenxe2x80x9d type, that is, provided with two reversible stands GR1 and GR2, shown schematically in FIG. 3, each having four grooved profiles (respectively from PS1 to PS4 and from PS5 to PS8).
Therefore, conventional rolling lines are not compact and require considerable investment to make civil engineering structures, such as foundations and the plant (sheds) for these lines, since such lines do not allow concentration of the roughing operations, upstream of the finishing train, in a limited area.
U.S. Pat. No. 5,904,061 discloses a method of rolling finished sections from a preliminary rolling group constituted by a vertical two-high reversing stand (VVG) followed by a horizontal two-high reversing stand (VHG) with two shaped grooves. The VVG provides only for a simple upsetting of the base and head of the rail section. The emerging rail section is rolled in a reversing operation after three or more passes in the universal stand and in two alternative grooves of an intermediate upsetting stand. The section is finish-rolled into a rail section in an additional pass through the universal stand. This known method provides that the starting product is already shaped as function of the final product to be obtained. The first profile of the VHG (i.e. WH1) is already shaped and the VVG is not exclusively used in combination with the first profile (WH1) of VHG, but also with the other profile (WH2). FR-A-2,529,480 discloses a method for rolling rail from a hot-rolled bloom having a square or rectangular cross section, wherein the method comprises the steps of breakdown rolling, universal rolling, which is effected by causing the bloom to travel through a plurality of stands making only a single pass on each stand, base-wheel rolling, head-wheel rolling and edging. The bloom is broken down into substantially H-shaped beam blank whose cross section is symmetrical with respect to the center line of its web. In the base-wheel rolling, the flanges of the blank corresponding to the head and base of the rail are respectively rolled widthwise and thicknesswise in three or more passes using a pair of horizontal rolls and a vertical roll, respectively. Also in this case the vertical stand (VE) performs only a simple upsetting of the heads of such H-shaped profile before entering the finishing section of the rolling line and, additionally, is not utilized in alignment with the grooved profile of substantially rectangular form.
DE-A-19743633 discloses a method of rolling finished sections from preliminary sections by means of roll stand arrangements which operate in reversing operation and include a compact rolling group composed of a first universal stand at the entry side and a second universal stand at the exit side and an intermediate edging stand arranged between the universal stands, and a roughing group arranged in front of the compact rolling group and composed of vertical non-reversing roll stands (VG) and horizontal roll stands (HG) having three shaped grooves. A rectangular preliminary section or a preliminary section having the approximate final dimensions is pre-shaped in the roll stands of the roughing rolling group in a number of shape changing passes and/or shape reduction passes. Subsequently, the section is further shaped in the compact rolling group in several shape changing passes or shape reduction passes in the universal stand on the entry side. Subsequently, the section is shaped into the finished section in the universal stand on the exit side or in the intermediate edging stand, possibly also with the use of the selectable grooves or the grooves of the roll stands located next to each other. In this rolling line, the vertical stand VG solely performs a simple finishing of the edges of the starting product. The first profile of HG has not a substantially rectangular shape, but it is shaped.
The present Applicant has devised and perfected the rolling method and line for rails or other sections according to the invention to overcome disadvantages of the state of the art.
One of the purposes of the invention is to obtain rails or other sections using a compact, simple and economical rolling line and method, wherein it is not necessary to rotate the bar being worked as it passes from one grooved profile of the rolling rolls to the other.
In accordance with the purpose, the rolling method and line according to the invention provide to use an edging stand only for the edging operations, thus leaving the roughing operations and the preparation of the shaped pieces to a single BDM stand, in order to reduce the equipment necessary for the roughing/preparatory rolling sequences.
The edging stand can be arranged irrespectively. upstream or downstream of the BDM stand, according to the starting material and the rolling sequence.
We thus obtain a very compact reversible roughing assembly which can be defined as a Reversible Compact Roughing Mill (RCRM).
Compared with the state of the art, the rolling method and line according to the invention have at least the following advantages: a very compact layout of the rolling line; a reduction in the main rolling equipment used and the relative operating spare parts; reduced investment costs thanks to the reduction of the mechanical and electrical equipment, and the civil engineering structures, such as the foundations and the plant; and concentration of the roughing operations for the billets/blooms in a limited area, with a consequent reduction in the times needed to handle the rolled product; an increase in productivity of the roughing zone compared with conventional solutions as in the state of the art; improved functioning of the zone where the stands are changed and prepared thanks to the limited bulk and weight of the equipment; and better control of the rolling temperature due to compacting the roughing area.
To be more exact, the edging stand used in the method and line according to the invention operates at a convenient distance with respect to the BDM stand, upstream or downstream thereof, on the same working axis and has the following characteristics:
The rolling rolls can be cantilevered or have a double support; the whole stand can be displaced both laterally and vertically to be positioned on the working axis or off-line, when it is not being used or for change-over operations; it is possible to use shaped rolling rolls or rings, or a plane table; the command motor can be positioned either below or laterally with respect to the rolling axis.